For a long time it has been known how to prepare and use supports, especially those made of porous inorganic matter, to fix microbial populations such as bacteria, yeasts, enzymes or others by adsorption or other phenomenon, and thus to constitute biological catalysts usable for multiple applications in the most diverse industrial and agricultural fields.
In other supports of fritted glass materials, crystalline materials such as spinel-zircon or cordierite have been recommended. It has been clearly specified that these products should have, with a rate of least 70%, average diameters of well delimited pores, such as 0.8 to 220 microns for a bacteria population and 1 to 140 microns for yeast cells; in French Pat. No. 78.26415 and U.S. Pat. No. 4,149,937, the declared granulometry for the supports was specified as about 0.7 to 1 mm.
It has also been found that in the case of some inorganic materials, the amount of biomass fixed per surface unit of the material and the stabilization in time of the biocatalyst obtained were not necessarily a function of the porosity of the product nor of the need to have at its disposal an average pore diameter at least equal to, and preferably several times greater than, a diameter of the microorganism to be fixed. The effectiveness of the catalyst can actually be profoundly affected by phenomena of restriction of accessibility, mechanical or physical, for the organisms. For example, in supports with great porosity, the enzymes which line the pore walls show very reduced activity specifically because of the composition of a diffusion boundary layer at the surface of the solid support, this layer constituting a barrier which slows down the reactions caused by the biomass.